File Encryption and Decryption using OpenSSL 🔒

Overview 📄

This project provides a C++ implementation for encrypting (sealing) and decrypting (opening) files using asymmetric encryption with OpenSSL. It demonstrates how to securely encrypt data using a public key and decrypt it using the corresponding private key.

Key Functions and Their Purpose 📌

1. read_data:

• Reads data from an input file stream into a buffer.
• Parameters:
  • processed_size: Size of data to be read, updated to the actual number of bytes read.
  • in_file: Input file stream to read from.
  • buffer: Buffer to store the read data.
• Returns true if reading is successful, false otherwise.

2. write_data:

• Writes data from a buffer to an output file stream.
• Parameters:
  • processed_size: Size of data to be written.
  • out_file: Output file stream to write to.
  • buffer: Buffer containing the data to write.
• Returns true if writing is successful, false otherwise.

3. seal_data:

• Encrypts (seals) data using a public key and a symmetric cipher.
• Parameters:
  • in_file: Input file stream containing the data to encrypt.
  • out_file: Output file stream to write the encrypted data.
  • public_key: Public key used for encryption.
  • symmetric_cipher: Name of the symmetric cipher to use.
  • context: Cipher context for encryption operations.
• Returns true if encryption is successful, false otherwise.

4. seal:

• Encrypts (seals) a file using a public key and a symmetric cipher.
• Parameters:
  • in_filename: Name of the input file to encrypt.
  • out_filename: Name of the output file to write the encrypted data.
  • public_key_filename: Name of the file containing the public key.
  • symmetric_cipher: Name of the symmetric cipher to use.
• Returns true if encryption is successful, false otherwise.

5. open_data:

• Decrypts (opens) data using a private key.
• Parameters:
  • in_file: Input file stream containing the encrypted data.
  • out_file: Output file stream to write the decrypted data.
  • private_key: Private key used for decryption.
  • context: Cipher context for decryption operations.
• Returns true if decryption is successful, false otherwise.

6. open:

• Decrypts (opens) a file using a private key.
• Parameters:
  • in_filename: Name of the input file to decrypt.
  • out_filename: Name of the output file to write the decrypted data.
  • private_key_filename: Name of the file containing the private key.
• Returns true if decryption is successful, false otherwise.

Usage Example 📘

int main() {
    assert(seal("fileToEncrypt", "sealed.bin", "PublicKey.pem", "aes-128-cbc"));
    assert(open("sealed.bin", "openedFileToEncrypt", "PrivateKey.pem"));

    assert(open("sealed_sample.bin", "opened_sample.txt", "PrivateKey.pem"));

    return 0;
}

Tools and Techniques Used 🛠️

• OpenSSL:
  • Utilized for cryptographic functions, including encryption and decryption.
  • Key functions include EVP_SealInit, EVP_SealUpdate, EVP_SealFinal for encryption, and EVP_OpenInit, EVP_OpenUpdate, EVP_OpenFinal for decryption.
• C++ Standard Library:
  • File handling using ifstream and ofstream.
  • Memory management using malloc and free.
  • String and stream manipulation.
• Error Handling:
  • Ensuring file streams are properly opened and closed.
  • Validating the success of cryptographic operations.
  • Cleaning up resources in case of failure to prevent memory leaks.

Concepts Applied 📚

• Asymmetric Encryption:
  • Encrypting data with a public key and decrypting it with a private key.
• Symmetric Encryption:
  • Using a symmetric cipher (e.g., AES-128-CBC) for the actual data encryption and decryption.
• Buffer Management:
  • Reading and writing data in chunks to handle large files efficiently.
• Resource Management:
  • Proper allocation and deallocation of resources to ensure no memory leaks.

Conclusion 📝

This project demonstrates how to implement file encryption and decryption in C++ using OpenSSL, showcasing the integration of cryptographic techniques with standard C++ file handling and memory management practices.